1. Field of the Invention
The present invention relates generally to the mobile Internet, and in particular, to a method for transmitting a data packet using an M-IP (Mobile-Internet Protocol).
2. Description of the Related Art
With a rapid increase in number of Internet users, there is a demand for various radio data services that can support high-speed data transmission (of over 144 Kbps even while the user moves at high speed) and can also support a multimedia service. Aiming to provide a worldwide roaming service, a radio multimedia service and a high-quality voice service, the IMT-2000 (International Mobile Telecommunication-2000) standard proposes a mobile communication technology capable of satisfying the above-stated requirements.
A mobile IP (M-IP) is a protocol, which has been standardized in Mobile IP WG (Working Group) of IETF (Internet Engineering Task Force), and enables a mobile node (MN, or a mobile terminal (MT)) to have a unique IP address to receive a data packet taking the IP address as its destination address (DA) at a given location on the Internet. The mobile IP consists of several network elements such as a home agent (HA), a foreign agent (FA) and a mobile node (MN). The mobile node, which is a mobile computer connected to the foreign agent, communicates with a correspondent node using an IP address assigned thereto. The home agent refers to a host or a router that manages the current location information of the mobile node and encapsulates/decapsulates the data packet. The foreign agent, located in a foreign network which the mobile node exists currently, decapsulates an encapsulated data packet transmitted from the home agent and provides the decapsulated data packet to the mobile node.
FIG. 1 illustrates a method for transmitting a data packet from a correspondent node to a mobile node according to the prior art. Referring to FIG. 1, in a location registration process, a mobile node (MN) 40 recognizes a neighboring foreign agent (FA) 30 through a radio channel and then sends a location registration request to the foreign agent 30. The foreign agent 30 then registers a location of the mobile node 40 in a home agent (HA) 20. The home agent 20 stores an IP address of the foreign agent 30 corresponding to the mobile node 40, to indicate that the mobile node 40 is located in the coverage area of the foreign agent 30.
To transmit a data packet for IP communication to the mobile node 40, a correspondent node (CN or a correspondent station) 10 in a wired network transmits to the home agent 20 a data packet whose destination address (DA) is defined as the address of the mobile node 40. The data packet is transmitted to the home agent 20 according to known IP routing by a default router (not shown) of the correspondent node 10. This is because its destination address is identical to the mobile IP address.
The home agent 20 extracts the destination address, i.e., the mobile IP address of the data packet, and transmits the data packet to the foreign agent 30 corresponding to the mobile node 40 having the extracted mobile IP address. As stated above, the home agent 20 encapsulates the data packet by tunneling and transmits the encapsulated data packet to the foreign agent 30. The foreign agent 30 extracts the data packet by decapsulation and transmits the extracted data packet to the mobile node 40 through the radio channel. Herein, the “tunneling” refers to a security technology for encapsulating an IP data packet with another IP data packet to redirect a datagam directed toward a certain IP address to another IP address.
FIG. 2 illustrates a method for transmitting a data packet from a mobile node to a correspondent node according to the prior art. Referring to FIG. 2, when at least one data packet is received from the correspondent node 10 through the home agent 20, the foreign agent 30 can detect an IP address of the correspondent node 10 from a source address of the received data packet. Thus, the foreign agent 30 can directly transmit the data packet to the correspondent node 10 through IP routing, without passing through the home agent 20.
When a transmission data packet is transmitted to the home agent 20 and a reception data packet is received from the foreign agent 30 as stated above, an incoming routing path of a data packet received at (or input to) the correspondent node 10 may be different from an outgoing routing path of a data packet transmitted from the correspondent node 10. This is because the IP routing transmits the data packet through different nodes at every transmission.
However, in a private network requiring security, a default router of the correspondent node 10 has a security function of comparing a port number of the incoming routing path with a port number of the outgoing routing path, and refuses the received data packet if they are different from each other. In this case, if the transmission data packet from the correspondent node 10 is transmitted to the home agent 20 and the reception data packet is received from the foreign agent 30, the reception data packet may be rejected by the default router of the correspondent node 10. In order to solve this security problem, the foreign agent 30 must transmit the data packet from the mobile node 40 only through the home agent 20.
When the data packet is transmitted through the home agent 20 as stated above, it must pass through a plurality of routing nodes, including the home agent 20, so that there occurs resulting in a time delay and it is not possible to guarantee the security between the home agent 20 and the correspondent node 10.